Power draw bar mechanism



Aug. 1, 1961 J. M. WALTER ET AL POWER DRAW BAR MECHANISM Original FiledJuly 28, 1955 4 Sheets-Sheet 1 i I o 0 i0 60-" FF 1 3 \J 59 0R v53INVENT 5 IATTORA/EYS.

g 1951 J.'M. WALTER ET'AL 2,994,250

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IN VEN TORS BY 21 Mm.

Aug. 1, 1961 J. M. WALTER ET AL 2,994,250

POWER DRAW BAR MECHANISM Original Filed July 2a, 1955 4 Sheets-Sheet 4 5e a 4 fi w fi 1 A kiwi 3W0 WTWM ATTOENEYS.

United States Patent 9 Claims. (Cl. 9011) This invention relates to adraw bar mechanism for securing a cutter to the rotatable spindle of amachine tool and for subsequently demounting the tool from the spindleto be interchanged with other types of cutters. The present applicationis a continuation of the co-pending application of John M. Walter andArthur H. Geyler, Serial No. 524,967, filed on July 28, 1955, nowabondoned.

Milling cutters of the type to which the present invention is directed,such as those used in large horizontal planer-type milling machines, areequipped with tapered shanks adapted to be interfitted with acorrespondingly tapered socket formed in the working end of the toolspindle. There is a substantial variation in the degree of taper whichtool designers and machine tool builders have developed to suit theneeds of particular machining operations. However, two standard tapersare now widely used in the industry, making it possible to supplyspindle sockets which will receive one or the other of the two standardcutting tool shanks. One of these standards provides a taper ofapproximately three and one-half inches per foot (National Standard) andis known as a non-sticking taper. This taper angle is quite steep and adraw bar necessarily is used toexert a constant pull on the tool shankto hold it in place in the spindle socket. As soon as the draw bar isreleased, the tool will drop out of the socket or can easily be removedsince the degree of taper was selected to provide this non-stickingquality.

On the other hand, where a greater degree of strength and rigidity isrequired, the spindle socket and tool shank is provided with a lessertaper, known as a sticking taper. One standard taper of this type (Brownand Sharpe) has a taper angle of approximately five-eighths of an inchper foot, as compared with the National Standard of three and one-halfinches per foot. Tools having a low taper of this order, upon beingforced into a correspondingly tapered spindle socket, become wedged orlocked and cannot be dislodged from it without the application of adriving force. Moreover, in the use of such tools, the reaction of thecutting edges uponthe work tends to drive the tapered shank more firmlyinto the socket, thus making the mounting of the tool in the spindleeven more secure and rigid. This action however also has the effect ofmaking the tool all the more ditficult to remove. Briefly therefore,inorder to dislodge the tool having a sticking taper, a power blow isrequired whereas the tool having a non-sticking taper can be dislodgedmerely by releasing the draw bar, allowing the tool to fall out of itsown weight.

The conventional draw 'bar, with which the spindles of most millingmachines, boring machines and the like are equipped, is in the form ofan elongated tie bolt extending axially through the spindle. Forengaging the 2,994,250 Patented Aug. 1, 1961 tapered shank of thecutter, one end of the draw bar is threaded and extends partially intothe tapered socket of the spindle, while the opposite end has a headwhich bears against the opposite end of the spindle. The end portion ofthe tapered tool shank includes a threaded bore to receive the threadedend of the draw bar, such that the draw bar, upon being tightened, pullsthe tapered shank into the socket and thus frictionally secures the toolin cutting position to the working end of the spindle. For removal ofthe tool, the draw bar is unthreaded; if the tool shank and spindle borehave a non-sticking taper, then the tool shank will be released when thedraw bar is loosened. However, if the shank and socket have a stickingtaper, then it is necessary to forcibly dislodge the shank by hammeringthe head of the draw bar, thereby to drive the shank from the socket.

This conventional draw bar arrangement is practical in machines of smallsize but is impractical and dangerous when machines are large and thecutters are heavy, as is the case with planer-type milling machines andthe like. In such instances, especially where the, spindle is mountedupon a vertical axis, two workmen may be required to make the toolchange, one to hold the cutting tool in place at the spindle, the otherto climb to the top of the spindle and rotate the draw bar for screwingor unscrewing its threaded end with respect to the tool shank, and alsoto hammer upon the head of the draw bar it necessary for dislodgment ofthe tool. More recently, machines having power driven draw bars havebeen provided, but an element of danger still persists in their usagebecause the depth of the threaded bore of the tool shank is limited;hence, during dislodgment of a sticking shank, the entire weight of thetool may be carried by only a few threads of the draw bar. Should suchthreads have been mutilated during prior usage, as is frequently thecase, then there is the likelihood that the tool will inadvertently dropfrom the spindle when the draw bar is partially unscrewed.

One of the primary objectives of the present invention has been toprovide a power-operated draw bar mechanism for tool spindles, which isusable with tapers either of the sticking or non-sticking type, whereinthe mechanism applies an unscrewing rotation to the draw bar forreleasing a non-sticking shank, combined with an axial force fordislodging a tool shank of the sticking type.

A further objective has been to provide a simplified draw bar mechanismfor use in conjunction with heavy cutting tools wherein tool dislodgmentmay be effected while a substantial length of threaded engagement ismaintained between the draw bar and tool shank to prevent accidentaldropping of the tool, and wherein tool mounting and demounting may beaccomplished in a rapid, convenient and virtually automatic manner.

Another objective has been to provide a draw bar mechanism having asimple cam and abutment arrangement for rendering the draw bar effectiveto cause forcible tool dislodgment upon rotation of the draw bar inunscrewing direction before the draw bar is unscrewed from the toolshank to any substantial degree.

Described briefly, a preferred structure according to the principles ofthe invention, essentially comprises two coaxial draw bar sections, onesection comprising a driver interconnected with a reversible powermotor, while the other comprises a tool-engaging section having athreaded rod or draw bar which screws endwisely into the bore of thetool shank. The two sections reside loosely within an axial bore in thetool spindle and comprise pull-in and push-out abutment surfacesrespectively cooperable with pull-in and push-out shoulders or abutmentsof the spindle. The contiguous ends of the two draw bar sections are inthe form of mating cam faces, generally of helical or lift profile, andthe said cams are configurated relative to one another to providepositive driving connection of the toolengaging section by the driversection in either direction of rotation of the latter. The contiguousends of the two draw bar sections also are configurated so that axialthrust may be imparted from the driver section to the tool-engagingsection. The two sections normally are spring biased toward one anotherand reside in contracted relationship within the spindle. Thus, thesections are normally collapsed, in that the over-all distance betweenthe abutments of the draw bar is least, when the driver section isrotated in the screw-in direction, and when the driver is rotated in thescrew-out direction the cam surfaces thrust the sections apart so thatthe distance between the abutments thereof approximates the distancebetween the opposed abutments on the spindle and then drives thetool-engaging section in screw-out direction relative to the tool shank.

When the motor is energized in the screw-in direction, the draw barsections remain in their contracted relationship and the draw barthreads itself into the tool shank and, with the pull-in abutments ofthe tool-engaging section in engagement with pull-in abutments of thespindle, then pulls the shank forcibly into the tapered socket.

When the driver section is rotated in the screw-out direction, the camfaces axially thrust the driver section from the driven section and alsoestablish a driving connection with the tool-engaging section, so as toinitially break loose its threaded engagement with the tool shank. Bothsections in unison now begin to move away from the tool as unscrewingproceeds, in consequence of which the push-out abutment of the driversection comes into engagement with the push-out stop on the spindle.This limitation of movement is translated through the axial orlongitudinal inter-engagement of the sections with one another as athrust upon the tool to disengage it from the socket. Preferably, thestops on the spindle are spaced apart a distance only slightly greaterthan the distance between the abu-tments on the draw bar sections whenthe sections are moved apart by cam action, so that the pushout stop ofthe driver reaches the push-out stop of the spindle before thetool-engaging section is appreciably unscrewed rfrom the tool shank. Ifthe taper is of the nonsticking type, the thrust force is unnecessaryand the mechanism simply unscrews the draw bar while the shankslidesoutwardly from its socket during continued rotation of the shaftsections. On the other hand, if the taper is of the sticking type, theunscrewing torque will screw the draw bar outwardly from the stickingshank, and the axial force will dislodge the sticking shank forsubsequent removal during continued rotation of the draw bar. If thefirst application of force fails to dislodge the stuck shank, then theoperation is repeated.

Various other features and advantages of the invention are brought outin greater detail in the following detailed description taken inconjunction with the drawings illustr-ating a preferred embodiment ofthe invention.

In the drawings:

FIGURE 1 illustrates the spindle head of the typical type of machinetool in which the invention is adapted to be employed.

FIGURE 2 is a cross sectional elevation of the quill and spindle of themachine showing the relationship of the draw bar par-ts uponpresentation of a tool to the spindle for mounting of the same.

& *FIGURE 3 is a view similar to FIGURE 2 showing 4 the draw barmechanism under power operation at the start of engagement of the drawbar with the tool.

FIGURE 4 is a view similar to FIGURE 2 showing the parts in thepositions they occupy during use of the tool upon the spindle.

FIGURE 5 is a view similar to FIGURE 2 showing the draw bar under poweroperation at the start of tool dislodgment.

FIGURE 6 is a view similar to FIGURE 2 showing the tool dislodged fromthe spindle but not yet disengaged from the tool.

FIGURES 7 and 8 are developed views of one type of means forautomatically changing the relative linear spacing of the fixed andmovable shoulders of the draw bar mechanism.

FIGURE 9 is a cross-sectional view taken on the line 99 of FIGURE 6..

FIGURE 10 is a diagrammatic view showing power drive apparatus for thedraw bar.

Rotary cutters of the type commonly used in large milling machines andthe like may Weigh anywhere from 10 to 200 pounds or more, and forattachment to a tool spindle they are provided with various standardizedtypes of shanks or mountings, each type having a threaded bore orlimited depth adapted to receive a draw bar. A typical tool constructionis illustrated wherein the cutter 1 (FIG- URE 2) is provided with atapered shank 2 having a central bore 3 which is threaded internally asat 4. The tapered shank 2 interfits within a tapered recess 5 of therotatable spindle 6 of the machine tool. In some instances, the spindleadditionally is equipped With one or more driving keys 7 which engagekeyways 8 in the cutter.

The taper of the tool shank and spindle bore shown in the drawingsrepresents either a sticking taper or a nonsticking taper for purposesof illustration. It will be understood that the draw bar mechanism ismounted interchangeably in tool spindles of either type without anychange in structure or principle of operation.

The spindle 6 may be rotatably journalled for axial movement in a quill9 mounted in the head 10 of the machine. Depending upon the type ofmachine, the head 10 (FIGURE 1) may be slidable upon a rail 11 which, inturn, may be vertically movable upon one or more columns, not shown. Byrelative horizontal and vertical adjustments of the rail 11, head 10,and quill 9, the cutter 1 may be brought to a predetermined positionwith respect to a work piece. In other types of machines the spindle maybe immovable axially and/or rotatable about a horizontal axis, but inany event, the spindle will be equipped with some sort of tie bolt tohold the cutter to the spindle during machine operation; hence, it willbe understood that the particular machine shown is only illustrative ofthe environment to which this improvement is addressed.

In the construction shown, the quill 9 is a tubular sleeve havingopposed, tapered roller anti-friction bearings 12 and 13 mountedtherein, and the spindle 6 is received in the inner races of thebearings, flanges 14 of the spindle being shouldered against theoutermost of the bearings while an adjustable collar 15 resides inabutment with the innermost of the hearings to hold the spindle againstaxial movement. The journal is provided with the usual dust cover '16 orthe like, and a similar journal arrangement, not shown, is employed atthe other end of the spindle.

The power draw bar apparatus of the present invention, indicatedgenerally at 17, is housed in a central, longitudinal bore 18 of thespindle which is also counter bored to provide an enlarged diameterportion 19. A shoulder 20 is provided at the juncture of the two boreswhich, in the embodiment shown, constitutes a pull-in seat for thetool-engaging shaft section. For wear purposes, a pair of bronze washers21-21 are rested on this shoulder J and for convenience the uppersurface of the top washer may be termed the fixed screw-in abutment.

Spindle 6 is provided with an opposed shoulder which may be termed apush-out or tool dislodgment abutment 22 spaced from the screw-inabutment 20 (FIGURE 2), and which, in the construction shown, isfurnished by a plug 23 which is threaded into a counter bore at theupper end of the spindle wherein the plug is keyed against rotation by ascrew 26. The abutment face 22 is constituted as the outer face of thelower of a pair of washers 27-27 which, like the washers 21-21 areinstalled for wear purposes.

The draw bar assembly '17 is an elongated unit made up of articulatedsleeve sections 29 and 30. The lower of these sections carries a pull-inshoulder 31 which is cooperable with the pull-in abutment 20 of thespindle (FIGURE 3), while the upper one comprises a push-out abutmentsurface 32 which cooperates with the fixed push-out abutment 22 of thespindle. A spreader cam means or coupling indicated generally at 33,which is explained in detail at a later point in the specification, isprovided through which distance across the abutments 31-32 or theirlinear spacing, may be shifted or altered automatically relative to thespacing or linear distance between the fixed abutments 20 and 22. Thisis accomplished as an incident to draw bar operation.

The tool-engaging section 29 of the draw bar assembly comprises aslender rod which is threaded as at 34 for direct connection with theinternally threaded socket 4 of the cutting tool 1, i.e., the presentinvention eliminates the need for a separate coupling between the tooland draw bar as is required in some of the past constructions. At itsopposite end member 29 carries a head or sleeve section 35 of enlargeddiameter which resides in the enlarged diameter portion 19 of thethrough bore of the spindle. Thus, abutment shoulder 31 is furnished bythe juncture of the two diameters. The slender rod portion of thissection of the assembly passes through the washers 21-21. The upperportion 30 of the assembly is tubular in form, the upper end terminatingas abutment surface 32 which is engageable with the fixed stop 22 of thespindle.

The contiguous ends of the upper and lower sections of the assembly 17provides the cam means 33. As shown in FIGURES 7 and 8, the terminalportion of each of the sections 29 and 30 comprises axially inclinedlift or throw surfaces 36, spaced upper and lower dwell faces 37 and 38,screw-out or driving dogs 39, and screw-in driver faces 40. The cam endsof the respective members are oppositely arranged and complement oneanother, it being understood that there may be as many lobes spacedapart peripherally as may be desirable; two have been found to beadequate to provide spreading movement of the shoulders 31 and 32suflicient to accommodate the depths of threaded socket holes furnishedin the usual standardized cutting tools. Also, by using the complementalcam configuration, the extensibility is doubled. The dwell surfaces,when in engagement, carry the axial load which the draw bar must sustainduring tool dislodgment. These members, of course, are wellfinished andhardened to carry the loads which they must sustain.

A tension spring 42, housed within bores of the driver and tool-engagingmembers, is employed to bias the mating cam surfaces toward one another.For this purpose, one end of the spring is carried on a pin 43 whichextends across the bore of the driver upper section 30, while theopposite end of the spring is sustained upon a pin 44 which extendsacross the bore in the head of the tool-engaging section 29.

The head 35 of the tool-engaging member 29 also carries a drag devicewhich brakes its freedom of rotation in the bore of the spindle 6. Asshown in FIGURE 9, the head 35 is longitudinally cross slotted, as at46, to receive a tube 47 which is slightly less in length than thediameter of the head. Opposed shoes 48-48 of friction fiber or similarmaterial are slidably mounted within the tube 47, and the inner ends ofthe shoes are counter-turned as at 50. A compression spring 51, mountedwithin the tube 47 around the counter-turned portions 50 of the shoes,urges them outwardly against the internal surface of the spindle bore19, thereby imposing a frictional load which generally immobilizes thetool-engaging section 29 of the assembly without actually preventing itfrom rotating under power drive.

Any suitable power driver may be employed to cause rotation of the uppersection 30 which constitutes a driver for the lower tool-engagingsection 29 of the draw bar assembly. In the construction shown, this isaccomplished as follows: A power input shaft 53, suitably journalled asat 54 upon the frame or head of the machine (FIG- URE 10), is splined asat 55 over a length corresponding generally to the range of travel ofthe quill 9 of the machine, and shaft 53 is axially aligned with thespindle 6 and draw bar assembly 17 therein. The splined portion of theshaft carries a collar 57 which is freely rotatable on the shaft 53 andupon which a sprocket 58 is rigidly mounted. Sprocket 58 is driven by achain 59 from a reversible electric motor 60. The end of the collar 57is provided with clutch teeth 61 and a cooperating clutch collar 62having clutch teeth 63 mounted on the splined portion of shaft 53 inslidable driven engagement therewith. Clutch teeth 61 and 63 arecooper-able with one another, but the clutch teeth are spaced apart soas to provide lost motion which allows the motor to gain speed beforebeing subjected to the load. Axial movement of collar 62 for clutchengagement and disengagement is provided by a clutch arm 64 which isactuated by a solenoid 65 or in other suitable manner. When the clutchteeth 61 and 63 are disengaged, sprocket 58 rotates freely on shaft 53,but when the clutch teeth are in driving engagement, collar 57 drivescollar 62 which, being splined to shaft 53, rotates the latter.

The opposite, endwise portion of shaft 53 is journalled in a centralbore in the spindle plug 23, passing through the compression washers27-27. The endwise portion of the shaft, splined as at 67, is in drivingengagement with an internally splined portion 68 provided at the upperend of the driver section 30 of the draw bar assembly. However, shaft53, at the portion in which it enters the spindle, is of reduceddiameter, providing a shoulder 70 against which a washer '71 is abutted.The spindle plug 23 is counter bored to provide a recess for a thrustwasher 72 which is keyed to the shaft 53 as at 73, and a compressionspring 74 surrounding the shaft 53 is interposed between the twowas'hens 71 and 72 at the other side of the plug 23. The lowermost ofthe compression washers 27 is fastened to the shaft 53 by means of pin75. Therefore, the shaft 53 is rotatable in the spindle 6 of themachine, but is movable axially in unison with the spindle. Spring 74biases the draw bar friotionally to the spindle so that the two tend torotate together. This arrangement helps to overcome the inertia of thedraw bar and associated parts which might otherwise tend to causeloosening of the tool if the spindle is accelerated rapidly by itsseparate drive.

Operation of apparatus When the draw bar assembly 17 is allowed to hangfree in the spindle 6, the screw-in shoulder 31 engages the top of theupper thrust washer 21 seated on the fixed abut ment 20 of the spindle(FIGURE 2). The drag shoes 48 are urged outwardly against the walls ofthe spindle bore, but the fall of the assembly to the position shown inFIG- URE 2 is permitted because of the cross slot through which theshoes extend.

As shown in FIGURE 2, the shank of a tool 1, introduced into the recess5 of the spindle, when lifted upwardly comes into engagement with thethreaded end 34 of the lower section 29 of the draw bar assembly priorto abutting engagement of the mating tapered surface of the tool shankand spindle recess. Therefore, further lifting of the tool in thespindle recess to the point where the tool shank engages the spindlerecess causes the whole draw bar assembly to be lifted vertically in thespindle to the position shown in FIGURE 3. The parts are so dimensionedthat in this condition the screw-out abutment shoulder 32 at the upperend of the driver section 30 of the assembly may clear but residegenerally adjacent the fixed upper abutment 22. During this period thecam 33 will be collapsed, and the sleeve sections are contracted.

Clutch teeth 61 and 63 are now brought into engagement by action of theclutch arm 64, and motor 60 is then started to drive shaft 53 in thescrew-in direction of rotation, as shown by the arrow in FIGURE 3.

Rotation of the shaft 53 in the screw-in direction causes rotation ofthe driver section 30, and the tool-engaging portion 29 is driventhereby through engagement of the respective screw-in faces 40-40 of thecam means 33 which are now mated with one another as shown in FIG- URE7. Therefore, the threaded portion 34 of the draw bar, having beenpositioned to engage the threads in the tool shank by resting thereon,now proceeds to thread its way into the tool shank. This motion isaccompanied by a downward axial movement of the entire draw bar assemblyalong the spindle toward the tool until the draw bar abutment shoulder31 comes into engagement with the fixed abutment face of the thrustwasher 21. This arrests axial movement of the draw bar assembly.However, further rotation thereof in the same direction causes the shankof the tool to be threaded and drawn inwardly into tight frictionalengagement with the tapered socket of the spindle. FIGURE 4, therefore,shows the tool fully socketed in the spindle and ready for use.

It is contemplated that the motor 60 be of the stall type, such that thedriving parts will not be unduly strained, or if desired, a lost-motionfriction-type clutch may be employed in place of the positive toothclutch in the power system. -It is also preferable that the motor 60 becontrolled by switches of the manually-sustained contact type, such thatthe motor will run only so long as the appropriate switch button is heldin.

By virtue of the operation of the apparatus in such manner that a thrustforce is delivered axially upon the cutter while the draw bar is insubstantial engagement with the cutter threads, mutilation of theendwise threads of the draw bar or the tool is minimized. On the otherhand, the simple, two-part construction of the draw bar, plus thepositive functions which it provides, enables the apparatus to beconstructed in a rugged and durable manner at low cost.

When it is desired to dislodge the tool from the socket, motor 60 isenergized to drive the input shaft 53 in the unthreading direction asindicated by the arrow in FIG- URE so as to unscrew the draw bar fromthe tool shank. It will be observed that at the start of this operation,the shoulder 31 of the tool-engaging section 29 is seated upon thethrust washers 21 through the pulling effect developed previously whenthe rod 29 was threaded into the tool shank to draw it forcibly into thespindle socket. As the input shaft 53 begins to rotate, the uppersection 30 rotates with respect to the lower section 29 which, as notedabove, is held stationary through its gripping effect with respect tothe tool. As the upper section rotates relative to the lower section,the inclined cam lift surfaces 36 of the two sections thrust the uppersection 30 upwardly along the spline 67 of the input shaft while itsupper end 36 approaches the screw-out abutment 22 of the spindle bore.At the end of the cam lift motion, the screw-out faces 39 of the camsurfaces engage one another (FIG- URE 8) so as to transmit the rotarytorque force from the upper section 30 to the lower section 29, thusinitially breaking the screw threaded engagement between the draw barand tool shank.

' The position of the two shaft sections at this point is shown inFIGURE 5. It will be observed in thisview that with the sections fullyextended, a clearance, as indicated at A, exists between the upper end32 of the upper section and the screw-out abutment surface 22. Theclearance A is slightly less than the height of the vertical screw-outfaces or dogs 39, as (indicated at B in FIGURE 5. Accordingly, upwardmotion of the upper section is limited to the extent of the clearance Ato prevent disengagement of the screw-out faces 39.

As explained earlier, the tapered shank and socket shown in the drawingsrepresents either a sticking or nonsticking taper. If the taper is ofthe non-sticking type, the mechanism simply unsorews the draw bar duringcontinued rotation of the sections 29 and 30, while the shank slidesoutwardly with respect to its socket.

FIGURE 6 shows the relationship of the parts with the socket partiallydislodged, the tool being slightly separated from the spindle socket andbeing suspended from the draw bar. It will be noted that the tool shankis engaged with a substantial number of threads at the end of the drawbar, thereby providing complete protection against the tool falling fromthe spindle. FIGURE 6 therefore represents the condition in which thetool is made ready to be removed physically from the machine. At thistime, the operator may be fully prepared to receive the tool when thedraw bar is completely released through further rotation of the shaft53. On the other hand, the tool may be allowed to drop to the platformof a tool transport of the type shown in the co-pending application ofJohn M. Walter et a1. Serial No. 514,475, filed on June 10, 1955, nowPatent No. 2,925,016, by means of which the tool may be transportedconveniently from the machine.

When the tool shank is provided with a sticking taper, the action isgenerally similar to that described above. However, in this case, theunscrewing torque applied to the draw bar as in FIGURE 5 will screw thedraw bar outwardly from the sticking shank, thus taking up the clearanceA above the section 3%) and causing the screwout abutments 22 and 32 toengage. At this point, the thrust force acts through the draw bar 29 todislodge the sticking shank from its socket for subsequent removalduring continued rotation of the draw bar. However, in exceptionalcases, the sticking may persist and in this case, the dislodgingoperation may be repeated by energizing the motor 60 in screwing andunscrewing directions so as to progressively unscrew and apply thrust tothe draw bar to break the frictional engagement between the shank andsocket. It will be observed that the clearance A allows the draw bar tobe slightly unscrewed before thrust is applied to the tool, and thatdislodging thrust is applied while a substantial number of threads areengaged so as to prevent mutilation of the threads. After the frictionalengagement is broken, continued rotation will bring the parts to therelationship shown in FIGURE 6 for subsequent removal of the tool fromthe spindle.

If desired or necessary, the present mechanism may be utilized todeliver impact blows axially upon the draw rod 29 to dislodge a stickingshank from the spindle socket. In this case, the driving system isarranged to impart rotary motion to the parts in an abrupt manner inforward and reverse directions. Thus, as shown in FIGURE 5, if the inputshaft is rotated abruptly in screw-out direction, the abrupt engagementof the screwout dogs 39 will apply a rotary momentum force to the drawrod in the unscrewing direction to break loose the screw threads and topartially unscrew the rod. Upon abrupt rotation of the parts in thereverse or screw-in direction, the tension spring 42 will propel theupper section 30 sharply in the downward direction by virtue of thesharply inclined throw surfaces 36 of the cams. These surfaces, combinedwith the rapid rotary motion, will cause the upper section to impart theimpact blow to the draw rod section which has been partially unscrewedto 9 permit the impact force ot act upon the sticking shank. Duringrotary motion in this direction, the drag shoes 48, by virtue of theirengagement with the spindle bore, hold the lower section 29 instationary position against the reaction of the inclined cam surfaces.

In the present disclosure, the shoulders 31 and 32 of the draw barassembly 17 are relatively movable through operation of the spreader cam33, while the spacing betweenthe shoulders 20 and 22, provided by thespindle bore is fixed. However, it will be understood that a reverseconstruction of any suitable form may be employed wherein the shoulderson the draw bar are fixed as to lineal spacing while those on thespindle may be changed as an incident to power operation of themechanism.

In utilizing the present structure upon a machine tool, an electricalinterlock preferably is provided to prevent operation of the draw barwhile the spindle is being driven during a machining operation. Also, asdisclosed in the aforesaid Walter application, Serial No. 514,475, nowPatent No. 2,925,016, an interlock may be provided to prevent poweroperation of the draw bar motor, particularly in tool dislodgingdirection unless or until a support is in place to receive the tool asit is disengaged. As shown in the co-pending application, the interlockcomprises a switch which normally interrupts the power circuit to thedraw bar motor, and closes the circuit when the tool support is inplace.

Having described our invention, we claim:

1. A machine tool including an elongated spindle having a boretherethrough communicating with a tool holder socket at one end adaptedto receive a tool holder having a shank fitting said socket forfrictional engagement therein, said shank having a threaded portionfacing said bore, said spindle bore having axially spaced abutmentsincluding a first abutment spaced from said socket and facing awaytherefrom and a second abutment further spaced from said socket andfacing said first abutment, a sectional drawbar comprising a firstsection and at least a second section in alignment therewith, said firstsection being threaded at one end for threaded engagement with thethreaded portion of said shank and having a first abutment spaced fromthe threaded portion for reaction with said first spindle abutment indrawing said shank into said socket, a reversible power drive means, toconnect said drive means to said second section, said first and secondsections having operable engagement at their adjacent ends, the otherend of said second section having a second abutment cooperating withsaid second spindle abutment, said operable engagement being constructedto rotate said first section into threaded draw engagement with saidshank when said section is rotated in one direction, said second sectionabutment being spaced from said second spindle abutment during saidrotation and said operable engagement being constructed to force saidsections apart upon reverse rotation of said second section with respectto said first section until said second section abutment is adjacentsaid second spindle abutment and then to stop said relative rotation totransmit the rotation to said first section to break a tight threadedengagement of said first section and said shank, whereupon anunthreading action takes place causing the said second abutments toengage and apply axial thrust through said sections, thereby to dislodgea stuck shank from the socket.

2. A machine tool including an elongated spindle having a boretherethrough communicating with a tool holder socket at one end adaptedto receive a tool holder having a shank fitting said socket forfrictional engagement therein, said shank having a threaded portionfacing said bore, said spindle bore having axially spaced abutmentsincluding a first abutment spaced from said socket and facing awaytherefrom and a second abutment further spaced from said socket andfacing said first abut ment, a sectional drawbar comprising a firstsection and at least a second section in alignment therewith, said firstsection being threaded at one end for threaded engage ment with saidthreaded portion of the shank and having a first abutment spaced fromthe threaded portion for reaction with said first spindle abutment indrawing said shank into said socket, a reversible power drive means, toconnect said drive means to said second section, said first and secondsections having operable engagement at their adjacent ends, the otherend of said second section having a second abutment, cooperating withsaid second spindle abutment, said operable engagement being con.-structed to rotate said first section into threaded draw engagement withsaid socket when said second section is rotated in one direction, saidsecond section abutment being spaced from said second spindle abutmentduring said rotation, said operable engagement comprising cam surfaceson the adjacent ends of said sections to move said sections apart uponreverse rotation of said second section relative to said first sectionuntil said second abutments are adjacent, shoulders on said adjacentends to stop relative rotation of said sections when said secondabutments become adjacent and to transmit said rotation to said firstsection to break a tight threaded engagement with said shank, whereuponthe unthreading of said first section with respect to a stuck shank andsocket will impart thrust through said second abutments and shoulders onsaid adjacent section ends to rigidly transmit said thrust back to saidstuck shank to dislodge the same.

3. A machine tool including an elongated spindle having a boretherethrough communicating with a tool holder socket at one end adaptedto receive a tool holder having a shank fitting said socket forfrictional engagement therein, said shank having a threaded portionfacing said bore, said spindle bore having axially spaced abutmentsincluding a first abutment spaced from said socket and facing awaytherefrom and a second abutment further spaced from said socket andfacing said first abutment, a sectional draw bar comprising a firstsection and at least a second section in alignment therewith, said firstsection being threaded at one end for threaded engagement with saidthreaded portion of the shank and having a first abutment spacedtherefrom for reaction with said first spindle abutment in drawing saidshank into said socket, a reversible power drive means, means to connectsaid drive means to said second section, said first and second sectionshaving operable engagement at their adjacent ends, the other end of saidsecond section having a second abutment cooperating with said secondspindle abutment, said operable engagement being constructed to rotatesaid first section into threaded draw engagement with said shank whensaid section is rotated in one direction, said second section abutmentbeing spaced from said second spindle abutment during said rotation,said operable engagement comprising cam surfaces on the adjacent ends ofsaid sections to move said sections apart upon reverse rotation of saidsecond section relative to said first section until said secondabutments are adjacent, shoulders on said adjacent ends to stop relativerotation of said sections when said second abutments become adjacent andto transmit said rotation to said first section to break a tightthreaded engagement with said shank, whereupon the 'unthreading of saidfirst section with respect to a stuck shank and socket will engage saidsecond abutments and develop a thrust force, and transverse shoulders onsaid adjacent section ends to rigidly transmit said thrust force back tosaid stuck shank to dislodge the same.

4. In a machine tool, the combination comprising a spindle having atapered socket for frictionally engaging the shank of a cutting tool, asectional draw bar assembly disposed for rotation and axial movementwithin said spindle, and having a threaded endwise portion adapted tothreadedly engage the shank of the cutting tool, power means forrotating said assembly in threading or unthreading directions to effectengagement and disengagement of said threaded portion relative to theshank of the tool, said spindle presenting spaced abutments, said drawbar assembly having spaced abutments respectively cooperable with saidspindle abutments, the dimensional spacing of the respective abutmentsnormally allowing limited axial movement of said assembly in saidspindle, and spreader means interconnecting the adjoining ends of saidsections, said spreader means adapted to provide a constant rotarydriving connection between the sections during rotation thereof inthreading or unthreading directions, said spreader means adapted tothread said endwise portion into draw engagement with said spindlesocket when the draw bar assembly is rotated in said threadingdirection, said spreader means being constructed to force said sectionsapart upon rotation thereof in said unthreading direction until saidrespective abutments of the spindle and draw bar assembly are broughtinto engagement, thereupon to unscrew said threaded portion from theshank and to devolp a thrust force acting through said draw bar assemblyin a direction to dislodge a stuck shank from the spindle socket.

5. In a machine tool, the combination comprising a spindle having atapered socket for frictionally engaging the shank of a cutting tool, adraw bar assembly comprising first and second sections disposed inalignment for rotation and axial movement within said spindle, saidfirst section having a threaded endwise portion adapted to threadedlyengage the shank of the cutting tool, power means for rotating saidassembly in threading or unthreading directions to effect engagement anddisengagement of said threaded portion relative to the shank of thetool, said spindle presenting spaced abutments, said draw bar assemblyhaving spaced abutments respectively cooperabie with said spindleabutments, the dimensional spacing of the respective abutments normallyallowing limited axial movement of said assembly in said spindle, andcam means at the adjacent ends of said sections, said cam meansinterconnecting the adjoining ends of said sections and adapted tothread said endwise portion into draw engagement with said spindlesocket when the draw bar assembly is rotated in said threadingdirection, said cam means being constructed to force said sections apartupon rotation thereof in said unthreading direction until saidrespective abutments of the spindle and draw bar assembly are broughtinto engagement, thereupon to unscrew said threaded portion from theshank and to develop a thrust force acting through said draw barassembly in a direction to dislodge a stuck shank from the spindlesocket.

6. In a machine tool, the combination comprising a spindle having asocket for frictionally engaging the shank of a cutting tool, said shankhaving a threaded portion facing said socket, a draw bar assemblydisposed for rotation and axial movement within said spindle, saidspindle having axially spaced abutment surfaces, said assemblycomprising a pair of sections presenting abutment surfaces respectivelycooperable with the abutment surfaces of said spindle, one of saidsections having a portion adapted to threadedly engage the threadedportion of said tool, reversibly operable power means for driving theother of said sections, the said assembly being normally axially movablebetween said spindle abutments, and a reversible operable drive clutchintercon necting said sections in axial load-sustaining relation, saidclutch comprising at least one inclined surface and follower cooperabletherewith in consequence of operation of said power means to cause axialshifting of one section of the assembly with respect to the other, saidinclined surface and follower changing the spacing of the abutmentsurfaces of the assembly and thereby delimiting axial movement of saidassembly during rotation of the assembly in tool dislodging direction toa range which is less than the range of axial movement of the assemblyduring rotation of the assembly in tool engaging direction, said clutchand abutment surfaces providing a thrust force acting through saidsections to dislodge a sticking shank during rotation of the sections inthe tool dislodging direction.

7. A machine tool including an elongated spindle having a socket forfrictionally engaging the shank of a cutting tool having a threadedportion, said spindle having an axial bore therein providing opposedthrust surfaces, a draw bar assembly mounted for axial and rotary motionin said spindle bore, said assembly comprising a pair of extensiblesections disposed in endwise relationship, one of said sectionscomprising a driver and the other constituting a tool-engaging section,said sections having inclined throw surfaces at adjoining ends thereof,said sections normally residing in a contracted position with said throwsurfaces inter-engaged and with the throw surfaces of the sections andspindle bore in spaced relationship to provide axial movement of thedraw bar assembly in the spindle bore, a second bore extending from saidaxial bore to said tool socket, a draw rod extending from saidtool-engaging section through said second bore to said socket and havingscrew threads formed on the end which projects into said socket,reversible driving means for rotating said driver section in screw-in orscrew-out directions, said throw surfaces providing screw-in abutmentsfor rotating the tool-engaging portion and draw rod in screw-indirection, thereby to engage and draw a tool shank forcibly into thespindle socket, and screw-out dogs at the outer end of said inclinedthrow surfaces, said throw surfaces and screw-out dogs camming saidsections apart then providing a driving connection between the sectionsupon rotation of the driver section in screw-out direction, whereby saidthrust surfaces engage and apply thrust to the shank of the tool todislodge the same upon rotation of the draw rod in screw-out direction.

8. In a machine tool which includes a spindle, a long tapered socket atthe end of the spindle, a cutting tool having a tapered end adapted tofit into said long tapered socket sutficiently closely to becomefrictionally affixed therein, a draw bar having one end thereof inthreaded engagement with the tapered end of the cutting tool, and meansfor rotating the draw bar in either direction to establish connection ordis-connection of the cutting tool with respect to the tapered socket,the improvement which consists in the combination of two draw barsections disposed within the spindle, each draw bar section having ashoulder thereon, said spindle having two internal abutments, one spacedfrom the shoulder of each draw bar section to permit limited axialreciprocation of the draw bar sections within the spindle, said draw barsections being interconnected at their adjacent ends to provide unitaryrotary motion of both draw bar sections, said adjacent ends beingconfigurated to provide a camming engagement in one direction ofrotation but not in the other, whereby the composite draw bar is ofminimum length when rotating in a direction to engage the tool in thesocket and of maximum length when rotating in a direction to disengagethe tool from the socket, the spacing of the draw bar shoulders andspacing of the spindle abutments being such that the draw bar exerts asubstantially immediate outward axial thrust on the tool when rotated inthe direction to disengage the tool.

9, In a machine tool which includes a spindle having a long taperedsocket at one end thereof, a cutting tool having a tapered end adaptedto fit into said long tapered socket sufficiently closely to becomefrictionally afiixed therein, a draw bar having one end thereof inthreaded engagement with the tapered end of the cutting tool, and meansfor rotating the draw bar in either direction to engage or disengage thetapered end of the cutting tool relative to the tapered socket, theimprovement which consists in the combination of two draw bar sectionsdisposed within the spindle, each draw bar section having a shoulderthereon, spring means interconnecting the two draw bar sections andbiasing the same axially toward one another, said spindle having twointernal abutments spaced from the shoulders of the draw bar sections,to

permit limited axial reciprocation of the draw bar sections within thespindle, said draw bar sections being interconnected at their adjacentends to provide a driving connection between both draw bar sections ineither direction of rotation, said adjacent ends being configurated toprovide a camming engagement in one direction of rotation but not in theother, whereby the composite draw bar is of minimum length when rotatingin a direction to engage the tool in the socket and of maximum lengthwhen rotating in a direction to disengage the tool from 10 the socket,said configurated adjacent ends of the draw bar sections adapted toprovide a constant rotary driving 14 connection between said sections inthe maximum or minimum length of the composite draw bar, the spacing ofthe draw bar shoulders and spacing of the spindle abutments being suchthat the draw bar exerts a substantially immediate outward axial thruston the tool when rotated in the direction to disengage the tool.

References Cited in the file of this patent UNITED STATES PATENTS2,667,820 De Vlieg Feb. 2, 1954 1 Patent No. 2994,2510

UNITED :STATES PATENT. OFFICE CERTIFICATE OF CORRECTION Au ust 1, 1961John M. Walter et a1 that error appears in the above numbered pat- It ishereby certified that the said Letters Patent should read as entrequiring oorrec'bion and corrected below.

Column 9, line 44 after "drive means insert, means column 10, line 5after "power drive means insert means column 11, line l8, for "devolp"read develop Signed and sealed this 23rd day of January 1962., v

(SEAL) Attestz;

ERNEST W. SWIDER Attesting Officer DAVID L. LADI) Commissioner ofPatents

